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Do NOT ever use rain water for an aquarium!!! In most parts of the world that stuff can kill fish because it is polluted! An aquarium is a closed system and rain water will buildup toxic materials from the water in the fish.

Knowledge is fun(damental)

A 75 gal with eight Discus, fake plants, and a lot of wood also with sand substrate. Clean up crew is down to just two Sterba's Corys. Filters: continuous new water flow; canister w/UV, in-tank algae scrubber!! Finally, junked the nitrate removal unit from hell.

OTOH, we still have tons of misinformed people that chuck salt into a community tank.

I think the key factor is knowing what kind of water you're starting with. If that's RO water then obviously you'll want some salt in the mix. If it's conditioned tap water then it depends on what your tapwater actually is.
Most successful discus keepers I know have switched to RO water and they add their preferred salt mix to it to bring it up to a certain conductivity value.

Do NOT ever use rain water for an aquarium!!! In most parts of the world that stuff can kill fish because it is polluted! An aquarium is a closed system and rain water will buildup toxic materials from the water in the fish.

I have used rainwater and haven't lost a single fish or shrimp doing so. In fact when I did two of my species bred. So, never is a bit strong, it can be done with a bit of care and common sense.

The article I posted was a general article on salt that I wrote a couple years ago, not written specifically to answer your question on discus. The article simply states the scientific data on what salt does to fish. I am not going to argue this, it is comparable to arguing that the earth is spherical with someone who believes it is flat. The scientific evidence is there, whether anyone believes it or not, it is still fact.

Talldutchie, you are referring to basic mineral salts in post #12 and there is no argument on that. The initial "salt" mentioned was common sodium salt being added to a freshwater fish tank with soft water fish, and as we all realize this is not wise. Enough said.

Byron Hosking, BMus, MA
Vancouver, BC, Canada

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]